This invention relates generally to security systems and more particularly to a method and apparatus for optically detecting activity within a monitored area.
Systems which monitor buildings for security purposes generally use ultrasonic, infrared or microwave techniques in order to sense activity in the area that is being monitored. An audible alarm is typically generated in order to alert the occupants and scare away the would-be intruder. The systems presently in use typically require sophisticated components which results in both high initial cost and high ongoing maintenance costs.
The present invention is directed to a method and apparatus which makes use of optical techniques to monitor a selected area and which responds to activity in the monitored area by increasing its illumination. This approach is advantageous not only for an intrusion detecting system but also for lighting systems in industrial and commercial areas such as corridors and warehouses. When the system is used for security, the increased light is sufficient by itself to frighten away prowlers. In industrial and commercial applications, corridors and warehouses can normally be illuminated only dimly but can automatically be fully illuminated when personnel such as watchmen are in the area.
It is the object of this invention to provide a method and apparatus for illuminating a selected area at a relatively low level of light under normal conditions and at an increased level of illumination when activity takes place in the monitored area. The automatic increase in the illumination of the monitored area leads prowlers to believe their presence has been discovered and thus causes them to flee the area without the need for an audible alarm signal. It is possible, however, for the system to be equipped with an audible alarm or an alarm system which signals a remote location such as a police station.
Another object of this invention is to provide a method and apparatus of the character described which has application both in a security system and in a general lighting system for industrial and commercial buildings such as warehouses and other largely unoccupied areas.
A further object of the invention is to provide a method and apparatus of the character described which can be implemented in a simple and economical manner and which consumes little energy in operation. The simplicity of an optical system as compared to ultrasonic, infrared or microwave systems leads to cost advantages. In addition, the flood lamp or other light source is normally operated at a low power level and thus consumes less energy than a light which is operating at full power.
A further object of this invention is to provide, in an apparatus of the character described, a control circuit which compensates for variations in the power line voltage. This compensation provides an extremely constant low level of illumination to the monitored area under normal conditions, thus allowing the system to have a much greater sensitivity to intrusions than otherwise would be possible.
Yet another object of the invention is to provide a method and apparatus of the character described which responds to either increased or decreased light reflected from the monitored area.
A still further object of the invention is to provide, in an apparatus of the character described, a control circuit which is arranged to minimize the effects of lightning.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.